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ANESTHETIC PHARMACOLOGY

The Role of Electrostatic Interactions in Governing Anesthetic Action on the Torpedo Nicotinic Acetylcholine Receptor

Douglas E. Raines, MD^*, and Robert J. Claycomb, BS

*Department of Anesthesia, Harvard Medical School; and Massachusetts General Hospital, Boston, Massachusetts

Address correspondence and reprint requests to Dr. D. E. Raines, Department of Anesthesia, Massachusetts General Hospital, 32 Fruit St., Boston, MA 02114. Address e-mail to DRaines{at}partners.org

Isoflurane and normal alkanols reduce the apparent agonist dissociation constant (K_d) of the nicotinic acetylcholine receptor (nAChR) at clinically relevant concentrations, whereas cyclopropane and butane do not. This suggests that electrostatic (hydrogen bonding and/or dipolar) interactions modulate anesthetic potency in this model receptor system. To further define the nature of these interactions, we quantified the potencies with which a heterologous group of general anesthetics reduces the nAChR’s apparent K_d for acetylcholine. We assessed the importance that an anesthetic’s molecular volume, ability to donate a hydrogen bond (hydrogen bond acidity), ability to accept a hydrogen bond (hydrogen bond basicity), and dipole moment play in determining aqueous potency. We found that aqueous anesthetic potency increases with molecular volume and decreases with hydrogen bond basicity but is unaffected by dipole moment and hydrogen bond acidity. These results suggest that anesthetics reduce the apparent agonist K_d of the nAChR by binding to a site that has a dipolarity and ability to accept hydrogen bonds that are similar to those of water, but a hydrogen bond-donating capacity that is less.

IMPLICATIONS: Anesthetics representing a wide range of chemical classes reduce the apparent agonist dissociation constant of the Torpedo nicotinic acetylcholine receptor with aqueous potencies that are governed by their molecular volumes and hydrogen bond basicities. However, neither their hydrogen bond acidities nor dipole moments influence aqueous potency.

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